Weatherseals, in automotive applications, are primarily used to provide a seal against wind, rain, noise and the like, in situations wherein glass and metal (or other materials) are in contact with each other (in fixed or movable situations), or in situations where metal components (or other materials) are in a movable relationship to one another, such as, for example, a door, trunk or hood opening with respect to the frame or body of the automobile.
Over the years, a wide variety of weatherseal materials have been proposed and used, including rubber, synthetic rubber, rubberized materials, plastics, elastomers and the like. A typical weatherseal might be fabricated of, for example, elastomers, which can be defined as a material which experiences large reversible deformations under relatively low stress. Some examples of commercially available elastomers include natural rubber, ethylene/propylene (EPM) copolymers, ethylene/propylene/diene (EPDM) copolymers, styrene/butadiene copolymers, chlorinated polyethylene, and silicone rubber.
Thermoplastic elastomers are elastomers having thermoplastic properties. That is, thermoplastic elastomers are optionally molded or otherwise shaped and reprocessed at temperatures above their melting or softening point. One example of thermoplastic elastomers is styrene-butadiene-styrene (SBS) block copolymer. SBS block copolymers exhibit a two phase morphology consisting of glassy polystyrene domains connected by rubbery butadiene segments. At temperatures between the glass transition temperatures of the butadiene midblock and the styrene endblocks the SBS copolymers act like a crosslinked elastomer.
In contrast, thermoset elastomers are elastomers having thermoset properties. That is, thermoset elastomers irreversibly solidify or “set” when heated, generally due to an irreversible crosslinking reaction. Two examples of thermoset elastomers are crosslinked ethylene-propylene monomer rubber (EPM) and crosslinked ethylene-propylene-diene monomer rubber (EPDM). EPM materials are made by copolymerization of ethylene and propylene, and are typically cured with peroxides to give rise to crosslinking, and thereby induce thermoset properties. EPDM materials are linear interpolymers of ethylene, propylene, and a nonconjugated diene such as 1,4-hexadiene, dicyclopentadiene, or ethylidene norbornene. EPDM materials are typically vulcanized with sulfur to induce thermoset properties, although they alternatively are optionally cured with peroxides.
Of specific interest in the process of the present invention, however, are weatherseals which comprise materials commonly referred to as thermoplastics and more particularly to “thermoplastic vulcanizates” (TPVs), and even more particularly to weatherseals made from extrudable TPVs.
Thermoplastic vulcanizates (TPV's) are polyolefinic matrices, preferably crystalline, through which thermoset elastomers are generally uniformly distributed. Examples of thermoplastic vulcanizates include EPM and EPDM thermoset materials distributed in a crystalline polypropylene matrix. One example of a commercially available material is Santoprene™. thermoplastic rubber which is manufactured by Advanced Elastomer Systems and is a mixture of crosslinked EPDM particles in a crystalline polypropylene matrix. These materials have found utility in many applications which previously used vulcanized rubber, e.g. hose, gaskets, and the like. In these applications, TPV's are noted for their ability to be processed as thermoplastics while retaining the excellent tensile and compression set properties of vulcanized rubbers.
Commercial TPV materials are typically based on vulcanized rubbers in which a phenolic resin or sulfur cure system is used to vulcanize, that is to crosslink, a diene copolymer rubber by way of dynamic vulcanization, that is crosslinking while mixing (typically vigorously), in a thermoplastic matrix. Sulfur or a phenolic resin is preferred over peroxide free radical cure systems because peroxide degrades a polypropylene or and crosslinks a polyethylene as well as the rubber and this is in turn limits the extent of rubber crosslinking that can occur before the entire mixture degraded or crosslinked and is no longer thermoplastic.
The thermoplastic material of use in the present invention, is preferably extrutable, and thus forms a thermoplastic extrudate. The thermoplastic extrudate is preferably a solid material which is essentially free of macroscopic voids, or alternatively, is a dense foam material having a density in the range greater than about 80% of that of the solid material. It should be noted, however, that the thermoplastic material of interest in the present invention is typically re-processable, unlike a thermoset resin.
By “extrudable” is meant that a material blend can be processed in an available, commercial extruder or injection moulding machine which provides internal mixing at a temperature in the range from, for example, about 180° C. to 240° C. with a residence time less than 5 min, preferably in the range from 30 sec to 2 min. In thermoplastics such as TPVs, which are typically “self-cured” and not physical blends, their combination of desirable elastic and thermoplastic properties depends on the respective amounts of “hard” and “soft” phases provided by each component, and the properties of each component. The polyolefin phase is the continuous “hard” phase in which the rubber “soft” phase is present as discrete particles. By varying the ratios of the components, one may provide desired hardness/softness, oil and temperature resistance, oxidation resistance, and extrudability, inter alia.
Through the use of thermoplastic materials, a weatherseal can be produced which is typically thinner and lighter than weatherseals made of prior art rubber or rubberized materials. Further, the thinner, lighter, thermoplastic weatherseals can provide reduced wind noise, while still providing good other weatherseal properties such as softness, abrasion resistance and low coefficients of friction.
The use of TPV materials as weatherseals has been previously described in, for example, U.S. Pat. Nos. 6,368,700 and 6,277,916. However, while TPV elastomers are used to produce weatherseals, the ever-increasing demands of the marketplace necessitate the development of processing thermoplastic weatherseals with improved properties.
In general, the prior art thermoset weatherseal materials would normally be bent to a desired shape by inserting the linear weatherseal extrudate into a bending press while heating the material to a temperature above its “heat-deformable temperature”. The press can then be used to press the material into the appropriate shape. Commonly, this appropriate shape would merely be a right angle bend so that the weatherseal material might be placed in, for example, the corner of a window opening in an automotive application.
Because of its thinner, lighter construction, and the differences in chemical thermosetting properties, thermoplastic weatherseals can be moulded up to 35% faster than prior art EPDM weatherseals. As such, use of thermoplastic weatherseals in bent applications could provide improved efficiencies.
However, thermoplastic extrudates are commonly used in linear, or straight-line applications, or in applications, with only minor amounts of bending. Typically, thermoplastic extrudates are not used in situations where bending to over 20° is required since the bending process can adversely affect the weatherseal. It has been observed that when thermoplastic weatherseal materials are bent using the above described bending process, a common occurrence is for the thinner sections of the extruded weatherseal to “buckle” and otherwise deform. If used in this condition, it would be difficult to achieve an effective, acceptable seal, and thus, leakage of water and/or an increase in wind noise would be possible, and would likely be probable.
The buckling effect is most noticeable on thinner sections (in cross section) of the thermoplastic material being bent, and the amount of buckling observed will be dependent on the material utilized, the heat deformation temperature for that material, the bending temperature use, the amount of time that the material is in the bending press, and the like. The buckling effect is typically characterized by a wavy, or non-linear deformation of a previously straight component of the extruded seal, after the bending operation. A typical example of this effect would be observed when, for example, an extruded thermoplastic weatherseal was bent 90° to fit in an automotive window or door application. After the bent area had been subjected to the heat and pressure encountered in a bending press, the thinner sections of the weatherseal would have a wavy appearance in the bent area.
To overcome this difficulty, it would be advantageous to provide a process for the bending of thermoplastic extrudate weatherseal materials, in a typical prior art bending device, which would provide a bent thermoplastic material with a reduced level of buckling, when compared to prior art process, and more preferably, would provide a process which eliminates the buckling effect essentially completely.